Electrical wave receiving system



' J/gauf 1939- I 1 D. A. WILBUR 2,183,232

ELECTRICAL WAVE RECEIVING SYSTEM Filed Aug. 18, 1938 2 Sheets-Sheet 1 CO"ed r os il l for //v l/EN TOR Dona/0 A. Wflbur' A 7- TOR/V5 YELECTRICAL WAVE RECEIVING SYSTEM Filed Aug. 18, 1938 2 Sheets-Sheet 2Patented Dec. 12, 1939 UNITED STATES ELECTRICAL WAVE RECEIVING SYSTEMDonald A. Wilbur, Troy, N. Y., assignor to American Industrial Research,Inc., Albany, N. Y., a corporation of New York Application August 1 8,

.14 Claims.

My invention relates to an electrical wave receiving system and moreparticularlyto means and methods of creating an electrical" carrier wavethrough the agency of the so-called side band or carrier and side bandwaves of modulated carrier energy and for combining the created carrierwave with the received electrical Wave in any desired relation.

Distortion of detected, modulated signals results from various causes,as will hereinafter appear, and the principal objects of my inventionreside in the provision of a method and means for substantiallyeliminating such distortion. More particularly, my inventioncontemplates the provision of an electrical wave receiving system inwhich the received signal and a carrier component, created in a localgenerator,'may be synchronized, or, correspondingly, the transformedfrequencies of the received signal as derived, for example, from anoscillator may be synchronized with the local generator, with the resultthat in both cases energy, from thelocal generator, at the carrierfrequency, may be added to the signal in an amount sufilcient that, upondetection, the difference frequency components resulting from reactionsbetween components of the signal, other than those due toreactionsbetween any component and the carrier, are effectively reducedor eliminated.

The principal objects of my invention, broadly, may be attained bydividing a signal, as received, or as obtained in a different part ofthe frequency spectrum by a reaction between the signal and the outputfrom a local oscillator, into two separate signals, creating thru theagency of one ofthese signals a component of a frequency equal to amultiple of the carrier frequency, separating this component, creatingfrom this separated component a component of a frequency equal'to' thecarrier frequency, adding "energy from this last mentioned component tothe second "of the above separated signals in an amount and relationsuch that upon detectionthe difference frequency components resultingfrom reactions between components of the resultant signal, other thanthose due to reactions between anyicomponent and the carrier, areelfectively reduced or eliminated. v i

correspondingly, a similar result is obtained. by creating thru theagency of one of the above mentioned separated signals a component of afrequency equal to a multiple of the carrier frequency, separating thiscomponent,.modulating this component by a signal of a frequency equal tothe same multiple of the frequency of a local os- 1938, Serial No.225,533

cillator, separating one of the side components produced by thismodulation, creating, thru the agency of this separated side component,a com ponent of a frequency equal to aJ-suitabl'e sub-- multiple of theseparated side component, modu 5 lating the second of the aboveseparated signals by this last created component, separating'theresulting modulation components which correspond in form to the originalsignal but have as their carrier frequency :one corresponding to thefrequency of the local oscillator, adding energy from the localoscillator to these components in an amount and relation such that upondemo'dulation the difference frequency components resulting betweencomponents of the resultant signal, other than those due to reactionsbetween any component and the carrier, are effectively reduced oreliminated. With the foregoing and other objects in view, my inventionincludes the novel elements and the 20 combinations and arrangementsthereof described below and illustrated in the accompany-' ing drawingsin which- Fig. 1 is a wiringdiagram of a fragmentary portion of anelectrical wave receiving circuit embodying one form of my invention;

Fig. 2 is a Wiring diagram illustrating another embodiment of theinvention; and j Fig.3 is a Wiring diagram of still another form of myinvention. In order clearly to describe my method of'pr'o cedure and theoperation of my circuit, consideration will be given first to thegeneral requirements which should be fulfilled and to their cause,and'cthen to the methods and'means of fulfilling these requirements; a

An electrical signal or wave such as referred to above may be produced"by modulating a sinusoidal energy wave, hereinafter called .the'carrierwave or carrier component, with a'simple or ec=the instantaneous valueof the voltage Ec=amplitude v v w=21rfc=angular frequency fe=frequency=time terms of voltage" be Let the intelligence wave be represented by:

( n m Sin (pm 'l Where-- m=1,2,3,...n em=the instantaneous value of thevoltage Em=amplitude of the m component pm=21rfm=angular frequency ofthe 121. component fm=frequency of the m component dm=initial phase ofthe m component t=time The resultant modulated signal will then berepresented by:

Where-- Ec sin wt=carrier component 12 cEE, cos pr) r] 1 =side-bandcomponents The reception of a modulated signal such as that symbolizedin Equation 3 involves the application of such signal or one of similarform to a demodulator or detector. In this process the angularfrequencies of all the components may remain the same or may be changedby the same amount as for example in the superheterodyne type ofreceiver. Thus we may represent the signal applied to the demodulator byEquation 3 where to then represents the angular frequency of the carriercomponent of the signal as applied to the demodulator.

r,s,=1,2,3, n

Thus it is evident that the additive result of the first two summationsis identical in wave form to the modulating signal as given in Equation2. These demodulation components shall hereinafter be designated as thedesired demodulation components and are described as being due to 2.

reaction between the carrier component and the side band components ofthe received signal.

It is also evident that the last two summations represent demodulationcomponents having no counterparts in the modulating signal as given inEquation 2. These demodulation components shall hereinafter bedesignated as undesired or distortion components and are described asbeing due to reactions between the components comprising the side bandcomponents of the received signal.

In considering the production of the desired demodulation components bya reaction between the carrier and side band components it is also Wellto note that should the phase of the carrier component be varied fromits original phase with reference to the side band components, theadditive result of the first two summations in Equation 4 will bevaried, or, as the phase of the carrier component is varied from 0 to180 from its original phase the amplitudes of the desired componentsdecrease becoming zero at a variation and then increase to theiroriginal magnitude but in an opposite sense at a variation. An identicalvariation in these amplitudes takes place as the phase of the carrier isvaried in the opposite sense. Also, should the amplitude of the carriercomponent be changed relative to the amplitudes of the side bandcomponents a corresponding change is produced in the amplitudes of thedesired components relative to the amplitudes of the undesiredcomponents. Thus, if for any reason the amplitude of the carriercomponent be reduced to zero, the amplitudes of the desired componentswill also be reduced to zero. Such a variation of the amplitude of thecarrier component, however, will produce no change in the amplitudes orphases of the distortion components.

Therefore, it follows that:

(a) A suitable carrier component is necessary for the production of thedesired demodulation components.

(17) The amplitudes of the distortion components may be reduced relativeto the amplitudes of the desired components by increasing the amplitudeof the carrier component relative to the amplitudes of the side bandcomponents.

A signal in which the amplitude of the carrier is reduced relative tothe amplitudes of the side band components, or in which the amplitude ofthe carrier becomes zero, or in which the phase of the carrier variesfrom its original phase with reference to the side band components, maybe produced, among other ways, by:

(a) Selective fading.

(b) Interference between ground and sky waves.

(0) Partial or total suppression of carrier at the transmitter.

Therefore, the aforementioned creation of a carrier or a wave of thecharacter of that of a transmitted carrier through the agency of theside band components, or the carrier component of a signal or both, maybe used to great advantage in the following situations.

Selective carrier fading, general signal fading and. interferenceresulting from natural phenomena may be corrected, even in the extremecase where no carrier component is present in the received signal, bythe creation of an appropriate carrier in the receiver.

Interference between transmitting stations duc'edmay then be'isolated bymeans of a selec-' maybe considerably reduced either by" reducing thetransmitted carrier wave energy with respect v to the; transmitted sideband energy or by completely eliminating the carrier wave energy in thetransmitted wave and then creating an appropriate carrier wave in thereceiver. e

- A considerable reduction in the power necessary to transmit a'signalmay be effected either disposed with respect to that of the carrier com-This component may then be isolated by means by reducing the transmittedcarrier wave energy relative to the transmitted side band energy or bycompletely eliminating the carrier wave enerbe represented in terms ofcurrent by 1'' cr Sin 1 2 c r Sin The component representedloyv Ec cos210i is produced by the action of the carrier component. I

The component represented by 2E 1' s cos pr+.pa) r+ s]; f 1:3

which reduces to is produced by reactions between those side bandcomponents whose frequencies are symmetrically ponent.

Thus a component having a frequency twice that of the carrier will beproduced either by a reaction between side band components or by areaction of the carrier component alone, or by both. Thus this componentwill be produced even though the amplitude of the carrier be materiallyreduced or made equal to zero.

Let this component be represented by of a selective filter, as forexample, one employing a quartz crystal. After isolation the componente20 may be used to producea component having an angular frequency w.

This maybe accomplished as follows. this component may be used tocontrol a synchronized oscillator or multivibrator whose output energywill contain a component having an angular frequency The, component soprolated signal.

ment and a selective filter.

First,

tive filter. Secondly, this component may be used to control a devicewhose output energy will contain a component of frequency one-half thatof the controlling component. The component so produced may then beisolated by means of a selective filter.

It is also to be noted that the component e20 regardless of whether itis produced by the carrier or side band components, depends for itsphase upon the phase of the original carrier en-' ergy which wasmodulated to produce the received signal. It should also be noticed thatthe controlling action of the component 620 on the devices described'above'may extend to the phase of the componentof output energy whoseangular frequency is w. Thus the phase of this component depends uponthe initial phase of the original carrier which was modulated to producethe received signal. This component shall hereinafter be calledthecreated carrier component. Therefore, since this created carriercomponent depends for its phase upon the phase of the aforementionedoriginal carrier, this phase may be made to maintain any desiredrelation to the phase of the original carrier by a suitable adjustreceived signal and isolated regardless of whether or not the carriercomponent is present in the received signal and this created carriercomponent may be combined with the signal to serve as the carrier or toaugment the carrier thereof as the case may be.

A corresponding method for obtaining the objects above pointed outconsists of creating a component by means of a local generator and thentranslating the frequencyand phase of the received signal so thatthelocally generated component fulfills the requirements for a suitablecarrier component for the received and trans- An example of this methodis as follows.

Let the received signal be diverted through two paths, one of the pathsincluding, as in the method described above, a non-linear circuit ele-From this is obtained, as shown above, a component 62c.

A locally generated component produced by an oscillator or other deviceis represented by The component cm is applied to a non-linear circuitelement, such as for example aso-called "frequency doubler. duced, amongothers, having twice the angular frequency of the applied component andmay be isolated by means of a selective filter. Let this component berepresented by It should be noted that the phase of this component willbe dependent upon that of the component em.

Now let the components 620 and 6210 be applied together to a non-linearcircuit element, such as, for example, a vacuum tube commonly known tothe art as a mixer tube. This will produce, among other components, acomponent whose angular frequency is equal to the sum of the angularfrequencies of the applied components and a component whose angularfrequency is equal to the difference of the angular frequencies oftheapplied components, Either of these com- A component is thusproponents may be isolated by means of a selective filter. Let thesecomponents, be represented by (9) CZdc -EZdc cos (Zia-2a) t (19)62sc=E2sc COS (2w+2a) it Let the component 6250 be isolated and appliedeither to control a synchronized oscillator or multivibrator whoseoutput energy will contain a component having an angular frequency(w-i-a) or to control a device whose output energy will contain acomponent of an angular frequency one-half that of the controllingcomponent. The component so produced may then be isolated by means of aselective filter, and may be represented by (11) esc Esc cos (w+a) t Itis also well to note that since such control may extend to phase, thephase of the component produced will be dependent both upon the phase ofthe original carrier energy which was modulated to produce the receivedsignal and upon the phase of the locally generated component.

The received signal in the second of the aforementioned two paths isthen applied simultaneously with the component @so to a non-linearcircuit element such as has been previously described.

This will produce among other components a band of components which maybe represented by and which may be isolated by means of a selectivefilter. Therefore, it is evident that these components represent afrequency translation of the received components to such angularfrequencies as permit the locally generated component elc to fulfill therequirements of a created carrier component; also that the phases of thetranslated components depend upon the phase of the locally generatedcomponent and upon the phase of the original carrier energy which wasmodulated to produce the received signal and that, therefore, by aproper adjustment of circuit constants the phase of the locallygenerated component may be made to have and maintain any desired valuewith respect to those of the frequency translated, received components.

It is to be noted that the component e2dc may be used in an analogousmanner to produce the same result and that in both cases the actiontakes place regardless of whether or not the carrier component ispresent in the received signal. Furthermore, various combinations of theabove methods may be used and it will be understood that the foregoingsteps are illustrative.

For a further illustration and a complete understanding of the methodand means employed in carrying out the same, including the operation ofthe circuits, of my invention, reference may be made to the followingdescription taken in connection with the drawings.

Referring to the drawings and first to Fig. 1, illustrating a circuitembodying one form of my invention, a signal, as received either with orwithout a carrier component and as amplified or translated in frequency,such as a signal of the character denoted by Equation 3, is impressedupon the grid of vacuum tube I. This vacuum tube is suitably energizedand functions as an amplifier. Thus the applied components appear ascurrent components in tuned circuit 4, resonant to these components.These current components are then transmitted to tuned circuit I, alsoresonant to these current components, by means of coils 5 and 6 and thecircuit including these coils and thus impressed upon the grid of vacuumtube 2. Vacuum tube 2 is suitably energized and is non-linear in itsplate current-grid voltage characteristic, and thus the square term ofthe series representing this characteristic will cause to be produced incoil 8 current components corresponding to those given by Equation 5.These latter current components are induced in the circuit to selectivefilter 9 by coil 8 and its associated coil in the filter circuit.Selective filter 9, for example a quartz crystal type of filter, passesto tuned circuit I0 substantially only the component corresponding to 62given in Equation 6. Tuned circuit i0 is resonant to this component andimpresses it upon multivibrator or controlled oscillator II.Multivibrator or controlled oscillator II is harmonically synchronizedby means of the applied component to oscillate in such a manner that itsoutput energy includes a current component whose angular frequency is w,or one-half that of the applied component. This current component isinduced in tuned circuit I3 by means of the coil therein and itsassociated coil I2 which is connected to the multivibrator H.

The signal current components present in tuned circuit 4 are alsoinduced in tuned circuit I3 by means of coils I5 and I6. Tuned circuitI3 is resonant to these components and thus also to the above mentionedcomponent of the output energy of multivibrator or controlled oscillatorThus a created carrier component is induced in tuned circuit I3 by meansof coil I2 regardless of whether or not a carrier component is presentin the received signal, and as previously shown, may be made tomaintain, by proper adjustment of circuit constants, any phase relationswith respect to the signal components induced in tuned circuit I3 bymeans of coil I6. In particular, these phase relations may be the sameas those existing between the carrier and side band components as givenin Equation 3.

The components present in tuned circuit I3 are impressed upon the gridof vacuum tube 3. This vacuum tube is suitably energized and func--tions as the usual detector or demodulator. Thus there will be producedin transformer I4 demodulation components corresponding to those givenin Equation 4 and it should also be evident that these will be producedregardless of whether or not a carrier component is present in thereceived signal. Also referring to Equation 4, it may be seen that theamplitudes of the desired demodulation components depend upon theamplitude of the carrier component Ec while the amplitudes of theundesired demodulation components are independent of the amplitude ofthe carrier. Thus the amplitudes of the desired components may beincreased to any desired degree relative to those of the undesiredcomponents by making Ec sufilciently large.

In Fig. 2, I have illustrated a circuit embodying a modified form of myinvention wherein the respective vacuum tubes are indicated generally bythe reference characters ZI to 26, inclusive. A signal, as receivedeither with or without a carrier component and as amplified ortranslated in frequency, such as given in Equation 3, is impressed uponthe grid of vacuum tube 2|. This vacuum tube is suitably energized andfunctions as an amplifier. Thus the applied components appear as currentcomponents in tuned circuit 21, resonant to these components. Thesecurrent components are then induced in tuned circuit 36, also resonantto these components, by coils 28 and 29 and thus impressed upon the gridof vacuum tube 22. Vacuum tube 22 is suitably energized and isnon-linear in its plate currentgrid voltage characteristic, and thus thesquare term of the series representing this characteristic will cause tobe produced in coil 3| current components corresponding to those givenby Equation 5. These components are induced by means of coil 3| and itsassociated coil in the circuit of a selective filter 32. Selectivefilter 32, for example a quartz crystal type of filter, passes to tuned.circuit 34 by means of coil 33 substantially only the componentcorresponding to age given in Equation 6. Tuned circuit 34 is resonanttothis component and impresses it in phase opposition upon the grids ofvacuum tubes23 and 24. Vacuum tubes 23 and 24 are suitably energized andare non-linear in their plate currentgrid voltage characteristics.

Tuned circuit 35, resonant to a component of angular frequency w, isconnected to the plates of vacuum tubes 23 and 24 in a so-calledpushpull configuration. Now, therefore, when due -to shot-efiect,thermal agitation, or any cause,

a current component having an angular frequency w is produced in tunedcircuit 35, this current component will be transmitted by means of coils36 and 31 and the circuit including these coils to tuned'circuit 38,resonant. to this component, and thus applied to the grids of tubes 23and 24 in phase agreement.

Let the above current component be represented by (13) icc=Icc cos wtand the component induced in tuned .circuit 38by 6cc=Ecc 005 wt Thusecc+e2c will be applied to the grid of one of said vacuum tubes 23 and24 Whi1e-6cc2c will be applied to the grid of the other. Thus the squareterm of the series representing the plate current-grid voltagecharacteristics will cause to be produced in the plate circuit of thefirst of these tubes, among other components, the

current component given in the following equation, (15), and in theplate circuit of the second of these tubes, among other components, thecurrent component given in the following equation, (16).

(15) 21:11 cos wt As is evident, the resultant current component intuned circuit will be the diiferencebetween components i1 and i2. Y

Let this be represented by I It should be noted that this currentcomponent is in phase agreement with the original component as expressedin Equation 13, and that therefore the above action may be madeself-sustaining. Moreover, it may be seen from a c'onsideraceivedsignal, and thus by properly adjusting the circuit constants,,may bemade to maintain any desired relation to the components of the receivedsignal.

This current component is transmitted by means of coils 39 and 40 andthe circuit including these coils to tuned circuit 41, resonant to theangular frequency of this component, and thus the component is impressedin phase agreement on corresponding grids 25a and 26a, respectively, ofvacuum tubes 25 and 26. The signal current components present in tunedcircuit 21 are transmitted by means of coils 42 and 43 and the 'circuitincluding these coils to tuned circuit 44, resonant to these components.Thus, as shown, these components are applied in phase opposition to thecorresponding grids 25b and 2612, respectively, of vacuum tubes 25 and26. Vacuum tubes 25 and 26 are suitably energized and operated in such amanner that there are produced incremental plate current componentsproportional to the product of the incremental potentials applied togrids 25a, 26a, 25b and 26b.

The constants of the circuits are so adjusted that the phase of thecomponent applied to grids 25a and 26a relative to that of thecomponents applied to grids 25b and 26b is such that the demodulationcomponents produced in the plate circuit of one of the vacuum tubescorrespond in form to those given in Equation 2. Hence, thosedemodulation components produced in the plate circuit of the othervacuum tube likewise correspond in form to those given in Equation 2,but are opposite in phase. nents of transformer 45 are obtained bytaking the difierence between the output components of these two vacuumtubes 25 and .26, the output components obtained from transformer 45 areequal 'to the additive result of the above mentioned output componentsof vacuum tubes 25 and 26 taken in like phase.

Moreover, it should be noted that demodulation components produced byreactions between components impressed on grids 25b and 26b will beidentical in form and phase, and thus produce no components of outputenergy in transformer 45.

Therefore, it is to be seen that, Whether or not carrier is present inthe received signal,'.de modulation output components are obtainedidentical in form to those used to modulate the original carrier energy.

In Fig. 3, I have shown a circuit embodying" another form of myinvention and the vacuum tubes therein are respectively indicatedgenerally by the reference characters 5| to 59, inclusive. A signal asreceived either with or without a carrier component and as amplified ortranslated in Since the output compo-1 frequency, such as given inEquation 3,is im-i.

upon the grid of vacuum tube 52. Vacuum tube 52 is suitably energizedand is non-linear in its plate current-grid voltage characteristic, andthus the square term of the series representing this characteristic willcause to be produced. in coil 64 current components corresponding tothose given by Equation 5.- These-latter current-2o .3

components are induced in the circuit of selective filter 65 by coil 64and its associated coil in the filter circuit. Selective filter 65, forexample a quartz crystal type of filter, passes to tuned circuit 66substantially only the component corresponding to en given in Equation6. Tuned circuit 66 is resonant to this component and impresses it upongrid 53a of vacuum tube 53. Vacuum tube 53 is suitably energized and isoperated in such a manner that there are produced, among othercomponents incremental plate current components which are proportionalto the product of incremental potentials applied to grids 53a and 53b.

The vacuum tube 59 together with its associate circuit elementsincluding tuned circuit 61 is suitably energized and operated as anoscillator. An output energy component 61c, as given in Equation 7, ofthis oscillator is applied to the grid of vacuum tube 58 by resistors 68and 69. Vacuum tube 58 is suitably energized and is nonlinear in itsplate current-grid voltage characteristic, and thus the square term ofthe series representing this characteristic will cause to be pro ducedin tuned circuit 19 a current component 6210 as given in Equation 8.Tuned circuit 10 is resonant to this component. This current componentis passed to tuned circuit 7!, also resonant to this component, and thusapplied to grid 53b of vacuum tube 53. It should be noted that the phaseof this applied component depends upon that of the component e10. Due tothe mode of operation of vacuum tube 53, there will thus be produced intuned circuit 12, among other components, the components can and ease asgiven in Equations 9 and 10 respectively. Tuned circuit l2, resonant tothe current component @250, isolates this component and it is induced intuned circuit 13, also resonant to this component. Thus this componentis applied to grid 54bof vacuum tube 54.

Each of vacuum tubes 54 and 55 is suitably energized and operated insuch a manner that there are produced among other incremental platecurrent components, components proportional to the product of theincremental potentials applied to grids 54a, 55a and 54b, 55b.

Tuned circuit 14, resonant to a component of angular frequency (w+a) isconnected in the plate circuit of vacuum tubes 54 and 55. when, due toshot effect, thermal agitation, or any cause, a current component havingan angular frequency (w +a) is produced in tuned circuit 14, thiscurrent component, is transmitted to tuned circuit 75, resonant to thiscomponent, and thus applied to grid 55a of vacuum tube 55. Coil 16,situated in the common cathode circuit of vacuum tubes 54 and 55,presents a high value of impedance to this component. Coil 16 thusprevents such a current component from appearing in the common cathodecircuit, and therefore results in effect in the application in phaseopposition of the component in tuned circuit 15 to the correspondinggrids 54a and 55a of vacuum tubes 54 and 55.

Let the above mentioned current component produced in tuned circuit Hicorrespond to isc given in Equation 18, following.

(18) sc=Isc cos (w-|-a)t Let the effective component applied to grid 54aof vacuum tube 5 correspond to est as given in Equation 11 and thatapplied to grid 55a of tube 55 correspond to es. Thus due to the mode ofoperation of vacuum tube 54, there will be produced in tuned circuit 14among other current components, a component corresponding to 3 as givenin Equation 19.

(19) 63:13 cos (w-l-a') t It should be noted that this component is inphase agreement with the original component isc as expressed in Equation18, and that therefore the above action may be made self-sustaining.Moreover, it may be seen from a consideration of the above-mentionedcomponents that this is the only self-sustaining action which may occur.It should also be noticed that the phase of the component expressed inEquation 19 depends upon the phase of the original carrier energy whichwas modulated to produce the received signal and upon the phase of theoutput energy of the local oscillator.

The component in tuned circuit corresponding to sc is applied to grid56a of vacuum tube 56. Vacuum tube 56 is suitably energized and operatedin a manner similar to that of vacuum tube 53. The signal currentcomponents present in tuned circuit 68 are transmitted to tuned circuitF9, resonant to these components, by means of coils Ti and 18 and thecircuit including these coils and thus applied to grid 55b of vacuumtube 56.

Due to the above indicated mode of operation of vacuum tube 56, therewill be then produced in tuned circuit 38, among other components, agroup of current components corresponding to etc as given in Equation12. Tuned circuit 86 is resonant to and isolates these currentcomponents. These isolated current components are then passed to tunedcircuit 8!, resonant to these components, and thus applied to grid 51aof vacuum tube 5?. Vacuum tube 51 is suitably energized and operated ina manner similar to that of vacuum tube 53. It should be noted that, aspreviously shown, these above-mentioned components depend in phase uponthe phase of the original carrier energy which was modulated to producethe received signal and upon the phase of the output energy of the localoscillator and thus may be made to maintain any desired relation to thatof the output energy of the local oscillator by proper adjustment ofcircuit constants.

A component of output energy of the local oscillator, corresponding toem as given by Equation '7, is transmitted from the local oscillator bycoils 82 and 8S and the circuit including these coils to tuned circuit84 and thus impressed upon grid are of vacuum tube 5'1. The constants ofthe circuits are so adjusted that the phase of the components applied togrid 51a. relative to that of the component applied to grid 51b is suchthat, among other demodulation components, components will be producedin the plate circuit of vacuum tube 51 and hence in the output circuitof transformer 85, which correspond in form to those given in Equation2.

Therefore, it is seen that, whether or not carrier is present in thereceived signal, demodulation output components are obtained of the sameform as those used to modulate the original carrier energy. Moreover, itshould be noted that since the desired demodulation components areproduced by reactions between the carrier component and the sidecomponents, while the un desired components are produced by reactionsbetween side components, the amplitudes of the desired components may bemade to have any desired relation to those of the undesiredcomponresulting from a change in the envelope of the ents by adjustingthe amplitude of the carrier component corresponding to em to theappropriate value. I

By my method of reception, distortion, due to lowering of the level ofthe carrier, including to zero level, and to change in its phaserelations with respect to the side components, and a consequent relativeincrease in the amplitude of the difference frequency terms due toreactions between side band components, as compared with the reactionsbetween carrier and side band components, cannot occur due to the factthat the carrier component may be maintained at any desired level andrelation by means of its introduction from a local generator. Also,distortion signal produced by a decrease in the amplitude of the carriercomponent or from its elimination, or from a change in phase, regardlessof the cause cannot occur since the desired shape of the envelope may berecreated by the addition of a suitable carrier component from the localgenerator. Distortion of the type described above is ordinarilynoticeable when interference occurs between the ground and sky waves inthe case of radio signals or when interference occurs betweensynchronized stations. Such distortion may also occur due to suppressionof the carrier component at the transmitting station or throughselective fading. Itshould be noted that distortion due to the abovecauses occurs regardless of the type of detector used and, hence, byemploying the method herein described, such distortion will beeliminated or, in any event, considerably reduced regardless of the typeof detector used.

Another desirable feature of my invention lies in the fact thatsynchronization between the signal applied to the final detector and thecomponent derived from the local oscillator is automatic and that in thecase where the last mentioned component is derived from a localoscillator such synchronization is independent of any reaction of theincoming signal upon the-local oscillator.

Still another desirable feature of my invention resides in the fact thatextremely sharp tuning may be obtained since either a balanced detectormay be used or a circuit of the character last described wherein nomodulated signal is applied to the final detector, and, therefore, ineither case there is no output from the detector except" when the signalis tuned in a fixed relation to the frequency of the filter. -Hence myinvention will provide automatic interstation noise suppression with noloss in sensitivity.

It is also well to note that the resonant and selective circuits may befixed in their tuning since in the superheterodyne type of receiver thep incoming signal may be shifted to any desired frequency and hence maybetuned in any desired relation to the selective filter mentioned in theabove description.

While the condensers illustrated in the draw-;

ings are shown as fixed condensers, it is to be understood that, in thefirst instance, in order to secure proper tuning, these condensers maybe adjustable. But once the circuits are properly tuned the condensersmay be permanently set and it will not be necessary thereafter to adjustthem.

While I have described my invention in its preferred embodiment, it isto be understood that the words which I have used are words ofdescription rather than'of limitation. .He'nce,

* comprising side components of the character of those of the receivedsignal but in which its carrier of the frequency of said created, firstcarrier wavemay be absent and means for combining said resultant signaland said first carrier wave.

2. In a device for receiving modulated signal energy which at leastinitially comprises carrier and side components, the combination withmeans for producing from the received signal first and second separatesignals having components corresponding to those of the received.

signal, of means. for producing through the agency of the first of saidseparated signals a signal comprisinga first component of a frequencysubstantially equal to the frequency of thecarrier of the receivedsignal multiplied by an integer, means for separating out said firstcomponent, means for creating a carrier wave, means for producingthrough the agency of said created signal a second component of afrequency substantially equal to the product of said integer and thefrequency of the created carrier wave, means for modulatingsaid'separated, first component by said second component, means forsep-' I arating out a side bandcomponent produced by saidmodulatiornmeans for creating through the agency of said separated sidecomponent a third I component of a frequency substantially equal to thefrequency of said separated side band component divided by'the saidinteger, means for modulating the second of said two signals by saidthird component, and means for separating from said modulated secondsignal components thereof corresponding in form to the received signalbut having as their carrier frequency a frequencysubstantially equal tothat of said created carrier wave. v

3. In a device for receiving modulated signal energy which at leastinitially comprises'carrier and side components, the combination withmeans for producing from the received signal first andsecondseparatesignals'having components corresponding to those of the receivedsignal, of means for producing through the agency of the first of saidseparated signals a signal comprising a first'component of a frequencysubstantially equal to the frequency of the carrier of the receivedsignal times an integer, means for separatingout said first component,means for creating a carrier wave, means for producing through theagency of said created carrier Wave a second component of a frequencysubstantially equal to the product of said integer ponent by said secondcomponent, means for separating out a side band component produced bysaid modulation, means for creating through the agency of said separatedside band. component a third component of a frequency sub-v stantiallyequal tol,the...frequency. of said .sepa-.,

rated side band component divided by said integer, means for modulatingthe second of said two signals by said third component, means forseparating from said modulated second signal components thereofcorresponding in form to the received signal but having as their carrierfrequency a frequency substantially equal to that of said createdcarrier wave, and means for combining said components so separated fromsaid modulated second signal and a component of said created signal ofknown character.

4. In a device for receiving modulated signal energy which at leastinitially comprises carrier and side components, the combination withmeans for producing from the received signal first and second separatesignals having components corresponding to those of the received signal,of means for producing through the agency of the first of said separatedsignals a signal comprising a first component of a frequencysubstantially equal to the frequency of the character of the receivedsignal multiplied by an integer, means for separating said firstcomponent, means for creating a carrier wave, means for producingthrough the agency of said created carrier wave a second component of afrequency substantially equal to said integer times the frequency ofsaid created carrier wave, means for modulating said first, separatedcomponent I by said second component, means for separating out a sideband component produced by said modulation and of a frequencysubstantially equal to the sum of the frequencies of said first, lastmentioned separated component and of the said second component, meansfor creating through the agency of said last mentioned separated sideband component a third component ofa frequency substantially equal tothe frequency of said last mentioned separated side band compo nentdivided by said integer, means for modulating the second of said twosignals by said third component, means for separating from saidmodulated second signal components thereof corresponding in form to thereceived signal but hav ing as their carrier frequency a frequencysubstantially equal to that of said created carrier wave, means foradding to said components so separated from said modulated second signala component of said created carrier wave, and means for demodulating theresultant signal.

5. In a device for receiving modulated signal energy which at leastinitially comprises carrier and side components, the combination withmeans for producing from the received signal first and second separatesignals having components corresponding to those of the received signal,of means for producing through the agency of the first of said separatedsignals a signal comprising a first component of a frequencysubstantially equal to the frequency of the character of the receivedsignal multiplied by an integer, means for separating said firstcomponent, means for creating a carrier wave, means for producingthrough the agency of said created carrier wave a second component of afrequency substantially equal to said integer times the frequency ofsaid created carrier wave, means for modulating said first, separatedcom ponent by said second component, means for separating out a sideband component, produced by said modulation and of a frequencysubstantially equal to the difference of the frequencies of said first,separated component and of said second component, means for creatingthrough the agency of said last mentioned separated side band componenta third component of a frequency substantially equal to the frequency ofsaid last mentioned separated side band component divided by saidinteger, means for modu" lating the secqnd of said two signals by saidthird component, means for separating from said modulated second signalcomponents thereof corresponding in form to the received signal buthaving as their carrier frequency a frequency substantially equal tothat of said created carrier wave, means for adding to said componentsso separated from said modulated second signal a component of saidcreated carrier wave, and means for demodulating the resultant signal.

6, In a device for receiving modulated signal energy which at leastinitially comprises carrier and side components, the combination withmeans for creating by employing side band components derived from thereceived signal a signal comprising a carrier wave of means forthereafter combining said created signal and the received signal wherebya resultant signal is produced comprising side components substantiallyof the character of those of the received signal and of said carrierfrequency, said resultant signal being characterized by the fact thatits carrier component may be absent, and means for combining with saidresultant signal carrier component from said created signal.

7. In a device for receiving modulated signal energy which at leastinitially comprises carrier and side components, the combination with anoscillator of means for creating by employing side band componentsderived from the received signal a signal having side band componentssubstantially corresponding in form to those of the received signal andof a frequency equal to the frequency of the oscillator frequency, meansfor adding energy from said oscillator to said created signal, and meansfor demodulating the resulting signal.

8. The method of improving the reception of modulated signal energy,which at least initially comprises carrier and side components, whichcomprises separating the received signal into a first and second signal,generating a carrier signal, producing by employing said first andsecond signal and said generated carrier signal a signal comprising sidecomponents substantially of the form of those of the received signal andsubstantially of the frequency of said generated carrier signal, addingenergy from said generated carrier signal to said last mentioned signaland demodulating the resultant signal.

9. The method of improving the reception of modulated signal energy,which at least initially comprises carrier and side components, whichcomprises separating the received signal into a first and second signal,generating a carrier signal, producing by employing said first signaland said carrier signal a third signal, combining said third signal withsaid second signal so separated from the received signal whereby toproduce a signal comprising side components substantially of the form ofthose of the received signal and substantially of the frequency of saidgenerated carrier signal, adding carrier energy from said generatedcarrier signal to said last mentioned signal and thereafter demodulatingthe resultant signal.

10. In a device for creating from a given signal wave a signalcomprising a component of predetermined character relative to said givensignal, the combination with cooperable means for producing from a firstsignal a second signal having a frequency equal to a predeterminedfraction of the frequency of said first signal, of means forreintroducing said second signal in said cooperable means wherebyproduction of said second signal will be maintained.

11. In a device for creating from a given signal wave a signalcomprising a component of predetermined character relative to said givensignal, the combination with cooperable means for creating from a firstsignal a second signal having a frequency equal to a predeterminedfraction of the frequency of said first signal, of means forre-introducing said second signal to said cooperable means and means foreffecting a substantially balanced operation of said cooperable meanswherebythose output components of said cooperable means produced by saidcreated second signal component alone are efiectively balanced and maybe eliminated.

12. In a device for receiving modulated signal energy which at leastinitially comprises carrier and side components, the combination withmeans for creating from the received signal a first component of afrequency substantially equal to a multiple of the carrier frequency, ofmeans for producing from said first component a second component of afrequency substantially equal to a sub-multiple of the frequency of saidfirst component; said last mentioned means being operable to produce asignal component only when signal energy is supplied thereto.

13. In a device for receiving modulated signal energy which at leastinitially comprises carrier and side components, the combination withmeans for creating from the received signal a signal comprising a firstcomponent of a frequency substantially equal to a multiple of thecarrier frequency, of means for separating out said first component,means for producing from said separated, first component a secondcomponent of a frequency substantially equal to a sub-multipleof thefrequency of said first component, said sub-multiple being the inverseof said multiple, and said last mentioned means being operable toproduce a signal component only when signal energy is supplied thereto,and means for combining said second component with the received signal.

14. The method of improving the reception of modulated signal energy,which at least initially comprises carrier and side components, whichcomprises generating a carrier wave, creating by employing a sidecomponent of the received signal a signal comprising side componentssubstantially of the form of those of the received signal and of thefrequency of said generated carrier wave but in which the carrier may beabsent, adding carrier energy from said generated carrier wave to thesignal so created and thereafter demodulating the resultant signal.

DONALD A. WILBUR.

